Posted: Sun Dec 15, 2013 2:16 pm Post subject:
power supplies etc --question for anyone who knows about thiSubject description: im not sure I completely understand the difference between the various

Ok, so I was reading another thread here on regulated power & circs etc and I realized I dont REALLY understand a LOT of what im up to. I could just keep on doing it, but once I start getting curious about something ill worry it until its figured out so my question is one requiring clarification I guess-
The deal is I (often) make things out of other things or combine various things and stuff I make myself. Actually thats not very clear..ok:
When I am, for instance, taking apart a voice changer and ripping the board out and then combining it with an oscillator ive made with a 40106 and a 324 filter and everything is running off 9v, I normally just throw a 9v regulator (7809) in after the battery and kinda cross my fingers and mostly it works out ok..BUT apparently, if id combined things with more Ma than it supplied or something, it WOULDNT work...so my question is:
why?
and, as an understandable correllary--what would?

I think what im doing is using things like 7809s as sorta similar to snap-on circuits or 'little bit' toys, thinking "well, this thingy does this over here..so itll probably do the same thing over there if I just stick it in that thingamajiggy cause it looks like its pretty much the same dealy as the thingy it was in to start with"
Obviously itd help me more to know what the hell im up to so I can do it more efficiently in the future.
Hopefully. (hope that doesnt sound crazy)

just fyi-A bit about my education-Ive got a JD (juris doctorate) and a MA (masters-arts) and BA and some technical degrees related to webdesign/development and programming and so forth-but the only hard science I have been educated in was biology in undergrad (minor) so I never really had any engineering classes and I just kinda throw myself at things until I get them to work...and often dont understand why or what im doing very well. Im attempting to remedy this so PLEASE forgive my TOTAL lack of technical terminology and possibly poor explanation of problem.
_________________www.newvoodoodesign.com
-my creations, bends & bendable pieces
-vintage parts & tubes, IC's & audio chips
-oddities & weird
newvoodoo.blogspot.com
-bending DIY/projects
-crap

A common 3 terminal regulator IC requires on it's input some 2.0 to 2.5 volts minimum above the regulated output voltage. That would mean a 9 volt regulator needs 11.0 to 11.5 volts on it's input in order to work correctly - or even at all. This is spelled out in the datasheet. LDO regulators are a special case. LDO stands for "low drop out". These regulators can withstand a lower input voltage, but there still must be some "headroom" between the input pin and output pin. This information is also in the datasheets. This means the even an LDO 9 volt regulator won't work properly when powered by a 9 volt source.

A 9 volt battery is already a sort of chemical regulator. It will stay at 9 volts until it is close to exhausted. So there really is no need for a regulator on a battery operated circuit.

Using wall-warts is a different story. These transformers (assuming AC wall-warts) have a voltage rating - but don't expect to get the rated voltage at all current flows. The more current you try to draw from an AC transformer, the lower the output voltage will go. In this case, you need a regulator to stabilize the output voltage. And as I stated above, the voltage in the input pin of the regulator should never fall below the input voltage spec'd in the datasheet (which is usually 2.0 to 2.5 volts above the spec'd regulated output voltage).

Datasheets can be a pain to read. They aren't pretty and there's lots of numbers. It's a good idea to take your time and read through them. You ought to be able to find information on the web regarding what the "symbols" mean. That said, datasheets are really your friends._________________FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.Fruit flies when you're having fun.BTW, Do these genes make my ass look fat?corruptio optimi pessima

ok i should have been clearer. I didnt necessarily mean a 7809 powered by a 9v it was a bad example, I meant im putting regulatrs in and using them as a 'fix all' when im combining multiple circuits, even when they have the same draw. I was wondering if that practice was correct, or even necessary--so I assume what I can get from what you said is there is no need for this with a 9v square battery but there IS with AC adaptors? and that that is for reasons of draw?_________________www.newvoodoodesign.com
-my creations, bends & bendable pieces
-vintage parts & tubes, IC's & audio chips
-oddities & weird
newvoodoo.blogspot.com
-bending DIY/projects
-crap

ok i should have been clearer. I didnt necessarily mean a 7809 powered by a 9v it was a bad example, I meant im putting regulatrs in and using them as a 'fix all' when im combining multiple circuits, even when they have the same draw. I was wondering if that practice was correct, or even necessary--

If all of the circuits you need to power need the same voltage, then you can just put them all in parallel. In this case regulators are not necessary. Use a star approach to the connection of "circuits" and your power supply. The center of the star is the power supply and the points are different circuits.

Quote:

so I assume what I can get from what you said is there is no need for this with a 9v square battery but there IS with AC adaptors? and that that is for reasons of draw?

With a brand new 9 volt battery, it will produce 9 volts up to a limit.

With an AC transformer, the transformer's voltage will change depending on the load. You would need to add a rectifier and filter to make DC, say 11 to 13 or more volts which is then applied to a regulator. The regulator is there because it expects it's input voltage to vary some._________________FPGA, dsPIC and Fatman Synth Stuff

Time flies like a banana.Fruit flies when you're having fun.BTW, Do these genes make my ass look fat?corruptio optimi pessima

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot vote in polls in this forumYou cannot attach files in this forumYou can download files in this forum

Please support our site. If you click through and buy from our affiliate partners, we earn a small commission.